1. Field of the Invention
The invention relates to a keyswitch suitable for use on a keyboard which comprises the data-entry equipment of a word processor, personal computer or the like.
2. Description of Related Art
A known keyswitch for use on such a keyboard is disclosed in U.S. Pat. Nos. 4,580,022 and 4,560,845. These keyswitches are provided with a rubber spring, which is attached to the bottom of the keytop facing downward, and a stem that is inserted into a key holder part built into the holder element for guiding and supporting up and down movement. The key switches also include, on the lower portion of the stem, a contact point with a bottom face. Also, switching components, such as a membrane switch constituting an electrical contact with the flexible sheet, are also attached to the bottom edge of the rubber spring.
In addition, in the keyswitch described in U.S. Pat. No. 4,580,022, it was suggested that between the bottom face of the keytop and the holder element a link element be installed that has the shape of an X when viewed from the side, so that when one edge of the keys, such as space bars, on which the flat area is large compared with the contact component, is pushed down, the keytop will move up and down evenly and in parallel, with no inclination. The link element links both central portions in free movement.
In keeping with the recent reductions in the thickness of keyboards, a large keystroke is demanded in order to secure a reliable keystroke as well as to facilitate keyboard operation, in spite of the flattening of the keyboard.
However, in the existing keyswitches, keytop vertical movement is guided for the sliding contact of the keyholder component and the downwardly protruding stem is attached to the bottom of the keytop. Because of this, the vertical dimension of the guiding, sliding movement of the stem within the holder component must be reduced when trying to reduce keyboard thickness. In doing so, the problem arises that when the key is pressed down, a misalignment may occur between the stem and the holder. As a result, the key does not operate smoothly and easily. If the sliding contact guiding dimensions are increased to prevent this, then the problem arises of the keystroke being too short. Thus, it is very difficult to simultaneously solve the two mutually contradictory problems of obtaining a large keystroke and reducing keyboard thickness.
In order to solve the above problems, the applicant has proposed a keyswitch, described below, in U.S. Pat. No. 5,280,147. As shown in FIG. 5, the keytop 100 vertical movement guidance method comprises a first link 101 and a second link 102 arranged, in profile, like an X, or scissor like, with both links linked to move freely at the intersection component 103. In addition, one of the free ends 106,107 and 108,109 of the second link 102 and the first link 101, respectively, are fastened in horizontal, sliding contact with the bottom face of the keytop 100 and holder element 104, respectively. The other of the free ends 110,111 and 112,113 of second link 102 and first link 101, respectively, are rotatably fastened to the bottom face of keytop 100 and holder element 104, respectively. Also, beneath the center of the intersection component 103 is a cap-form rubber spring 105 having a resilient shape-changing capability. When the top 100 is depressed, the guiding means intersection component 103 causes the rubber spring 105 to undergo resilient shape-changes and the switching component associated therewith performs a switching operation.
However, with a keyswitch of such a design, the free end 112,113 of the first link 101 centers on the place on the holder element 104 that forms the rotational axis for the purpose of movement capability, and the intersection component 103 moves in an up and down motion. In addition, the rubber spring 105 shape is formed based on it being pressed down in a straight line by the intersection component 103. In other words, the upper face of the head of the cap shaped rubber spring is formed in a horizontal shape.
Thus, when the upper face of this type of rubber spring head portion is depressed in a downward slant direction by the intersection component 103, the degree of resilient shape change of the dome component (the dome component's seated position shape-change degree) of the rubber spring misaligns greatly relative to the near side and the far side of the rotation point of the first link 101 and problems arise in terms of the functioning of the depressed key, such as the switching operation relative to the switching component of the lower portion of the rubber spring.
Because inaccuracies arise in the position of the rubber spring which covers the switching component due to tight tolerances, there is the problem of imperfections in switching operation relative to the switching component of the lower portion of the rubber spring.
Also, there is the problem of the actual thickness of the rubber spring, which covers the switching component, becoming an obstacle to reducing the thickness of the keyboard.